In many industry branches, there is a growing need for thin, hard layers having defined physical and chemical properties that are to protect components and surfaces of materials from wear or corrosion. Conventional layers are made of one or more plies having different compositions, quality characteristics, and functionalities.
For this purpose, in conventional plasma spraying methods, powdery, micro-scale particles are introduced in a low vacuum up to an almost atmospheric pressure region into a plasma jet source or a plasma jet, partially fused and vaporized there, and then plated on a substrate in a targeted manner at a high speed. Consequently, layers having different functionalities are deposited at relatively high deposition rates yet do not attain the homogeneity and compactness of typical PACVD layers (physically aided chemical vapor deposition) or CVD layers. However, the advantages of the plasma spraying are the highly localizable coating and high deposition rates.
In plasma spraying, the plasma jet is typically generated using direct voltage. However, new developments using inductive high-frequency coupling-in are also conventional. The latter has the advantage that the introduced powder particles have a longer dwell period in the plasma jet and are consequently more intensely fused.
Therefore, it is described in E. Pfender and C. H. Chang's, “Plasma Spray Jets and Plasma-Particulate Interaction: Modelling and Experiments” symposium volume of minutes from plasma technology workshop VI, TU Illmenau, 1998, to produce a plasma in a plasma jet source via externally applied high-frequency alternating currents and an inductive high-frequency coupling-in using a coil in a cup-shaped, cylindrical torch body, the plasma exiting the plasma jet source in the form of a plasma jet. It is also known from there to use helium, argon, or oxygen as the plasma gas to which a metallic powder may be added, so that, analogously to the known plasma spraying, these particles are superficially fused in the plasma jet, the particles are then deposited on a substrate outside of the plasma source.
The disadvantage of this method is first the high roughness and low mechanical strength of the deposited layers, which is due to the fact that the supplied powder particles in the plasma jet are only subjected to the high plasma temperatures of partially more than 9000 K for a short time due to the high flow velocity of the jet, so that they are not completely fused but only superficially fused. The supplied particles do not fuse and break up to an atomic or molecular level or to the level of nano-scale clusters. Therefore, such layers are not suitable as thin wear-protecting layers or hard material layers having a layer thickness of several micrometers. Furthermore, the composition of such deposited layers has been largely limited to metals and metallic oxides to date.
It is also conventional to deposit thin and high-grade wear-protecting and corrosion-protecting layers from the gas phase in the high vacuum using PACVD processes (physically aided chemical vapor deposition) or PVD processes (physical vapor deposition). PACVD and CVD methods are distinguished by qualitative, high-grade, dense, compact, and homogenous layers. However, the deposition rate is low since the deposition results from atomic growth. S. Veprek's “Theoretic concept for the design and practical preparation of new, thermodynamically stable, super-hard composite materials”, status seminar “Surface and layer technologies”, Würzburg, VDI technology center, 1997, volume 1, pgs. 27 and 28, describes on the basis of theoretical considerations depositing new, super-hard layers on substrates, e.g., steel substrates, with the help of a plasma CVD or a plasma PVD method. These materials are produced by combining a nano-crystalline, hard transition metal nitride MenN with amorphous Si3N4. The deposition occurs between 500° C. and 550° C. Further details about this concept are described in S. Veprek et al., Appl. Phys. Lett., 66, (1995), pg. 2640ff.
As a result of these nano-crystalline materials in an amorphous matrix, partially the hardness of a diamond is to be able to be achieved according to theoretical calculations.